#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int N = 210, INF = 1e9;

int n, m, q;
int d[N][N];

void floyd() {
	for (int k = 1; k <= n; k ++ ) 
		for (int i = 1; i <= n; i ++ )
			for (int j = 1; j <= n; j ++ )
				d[i][j] = min(d[i][j], d[i][k] + d[k][j]); 
} 

int main() {
	scanf("%d%d%d", &n, &m, &q);
	
	for (int i = 1; i <=n; i ++ ) 
		for (int j = 1; j <= n; j ++ ) 
			if (i == j) d[i][j] = 0;
			else d[i][j] = INF;
			
	while (m -- ) {
		int a, b, c;
		scanf("%d%d%d", &a, &b, &c);
		d[a][b] = min(d[a][b], c);
	}
	
	floyd();
			
	while (q -- ) {
		int a, b;
		scanf("%d%d", &a, &b);
		
		int t = d[a][b];
		if (t > INF / 2) puts("impossible");
		else printf("%d\n", t);
	}
	
	return 0;
}